1. Field of the Invention
The present invention relates to a robot system using a robot to load and unload (or place and remove) a workpiece into and from a machine tool.
2. Description of the Related Art
Known in the art is a robot system using a robot to mount a workpiece to a predetermined mounting portion of a molding machine or a machining center or other machine tool or remove a workpiece finished being processed from the mounting portion. Using such a robot system, it becomes possible to automate processing of a large number of workpieces by a machine tool.
A robot for loading and unloading a workpiece into and from a machine tool uses a mechanism combining linear movement axes and swivel arms. In particular, as a machine for taking out molded articles, at the present, Cartesian coordinate robots combining linear movement axes are generally used. While such a robot has the merit that compared with a swivel arm, complicated coordinate conversion at the time of control becomes unnecessary and the operation is easy to understand, it has the demerits that the robot easily becomes large, in particular the total height easily becomes greater, and transport separate from the molding machine easily become necessary.
FIG. 6 schematically shows a conventional robot system using a robot 50 combining swivel arms. A machine tool 60 is provided with a door 61 through which a workpiece 70 is loaded and unloaded. Robot 50 is arranged so that a base member 51 fixed to the floor surface is positioned at the front of door 61. This makes it possible to use simple, compact configuration robot 50 for efficient loading and unloading operation in machine tool 60. This is because if base member 51 is arranged at a position offset from the front of door 61, the distance from base member 51 to the inside of door 61 is longer and it tends to be necessary to lengthen the arm more, etc. Further, the arm would enter door 61 at a slant, and therefore structurally areas would easily arise inside door 61 which the front end of the arm could not reach. To position workpiece 70 at the desired area, an additional mechanism etc. tends to become necessary. For example, when robot 50 is arranged at the left side from door 61 of FIG. 6, in the illustrated configuration, the front end of the arm cannot reach the inside of the left side of the space in door 61.
Further, another conventional robot system using a robot combining swivel arms for loading and unloading a workpiece into and from a machine tool is disclosed in Japanese Unexamined Patent Publication No. 10-95028. In this prior art, the robot is mounted on the machine tool. In this case as well, the robot can be placed at a suitable position near the mounting portion for the workpiece, is simple and compact in configuration, and can be configured to enable suitable loading and unloading operations.
Further, Japanese Unexamined Patent Publication No. 6-106445 and Japanese Patent No. 3865703 disclose a robot system configured to enable a robot to move along rails extending among a plurality of machine tools and to load and unload workpieces into and from a plurality of machine tools by a single robot. In this case, suitable loading and unloading operations can be carried out by moving the robot to suitable positions with respect to the machine tools.
In the robot system shown in FIG. 6, when at the time of changing workpieces 70, at the time of maintenance, etc., a worker sometimes performs work at machine tool 60. In this kind of work, it is often necessary to adjust and inspect the mounting portion, holding mechanism, etc. for workpiece 70, and therefore such work is usually performed at the front of door 61 of machine tool 60. For this reason, in machine tool 60, an operating panel 62 is provided at the side surface where door 61 is provided. At the time of this type of work, if robot 50 were at the front of door 61, the work space would be narrow and work would be difficult.
On the other hand, in the configuration disclosed in Japanese Unexamined Patent Publication No. 10-95028, a robot for loading and unloading a workpiece into and from a machine tool is arranged on the machine tool and therefore, at the time of maintenance and other work, the robot will never cause the work space to become narrower. However, a robot which can be arranged on a machine tool is limited in weight and size and therefore, when handling a large workpiece, it is difficult to use such a configuration. Further, since it is necessary to make the robot comparatively small, the processing range of the robot also tends to become narrower. For this reason, there also tend to be limits to the layout of the device for supplying and carrying out the workpieces.
Further, as shown in Japanese Unexamined Patent Publication No. 6-106445 and Japanese Patent No. 3865703, if the robot is configured to be movable along rails, at the time of maintenance and other work, it is possible to make the robot move to secure the work space at the front of the door of the machine tool for loading and unloading workpieces. However, in a configuration using one robot for one machine tool, using rails for movement of the robot is considerably costly and not necessarily preferable.